The proposed work focuses on selected aspects of parenchymal mechanics, and on the interactions between lung surface forces, tissue stresses, embeddded airways and blood vessels, and airway fluid. Factors influencing gas trapping in lungs are to be investigated in rabbits, rats and guinea pigs. Trapping appears to be due to two phenomena: massive bronchoconstriction as in the excised guinea pig lung, or, massive peripheral airway foaming as in the excised rat lungs. Tissue hydration shifts certain segments of the lung's elastic recoil curve, and this in turn affects airway and vessel caliber. These interdependent relationships will be examined in dog lobes. Collateral pathways in dog (and probably man) are modulated by mechanical, chemical, and pharmacological influences. Neither the exact location of collaterals nor the basis of this responsiveness are well-understood; these will be examined as well in this proposal.